The present invention relates to a small sized image pick-up lens using a solid image pick-up element such as CCD type image sensor or CMOS type image sensor, image pick-up unit and mobile terminal provided therewith.
Recently, following making into high performance and size reduction of an image pick-up apparatus using a solid image pick-up element such as CCD (Charge Coupled Device) type image sensor or CMOS (Complementary Metal Oxide Semiconductor) type image sensor, a mobile phone or personal computer provided with the image pick-up apparatus is spreading. Further, for an image pick-up lens mounted in these image pick-up apparatus, a requirement for the further size reduction is increased.
As an image pick-up lens for such an application, from a reason that it can be made into the high performance and further appropriate for the size reduction, as compared to the lens of 1 or 2 lens composition, an image pick-up lens of 3-lens composition composed of, in order from an object side, a positive first lens, positive second lens, and negative third lens, is well known. These image pick-up lenses are disclosed in, for example, Patent Documents 1, 2.
[Patent Document 1] Tokkai No. 2003-322792
[Patent Document 2] Tokkai No. 2004-37960
However, although the image pick-up lenses disclosed in Patent Documents 1, 2, are types appropriate for the size reduction, because Abbe's number of a lens forming the negative third lens is more than 55, and the difference of Abbe's number to the lens material forming the positive first lens and second lens is small, there is a tendency that the on-axial chromatic aberration becomes under correction.
Furthermore, in the image pick-up lens disclosed in Patent Document 2, because a composite focal length of the second lens and the third lens, arranged on the image side from an aperture stop, is a negative value, an exit pupil position is too close to the image pick-up element, a chief ray incident angle (an angle formed between the chief ray and the optical axis, and when the chief ray is parallel to the optical axis, it is 0°) of the light flux image formed on the peripheral part of the image pick-up surface of the image pick-up element, is larger than 45°, and as the image pick-up element, when the solid image pick-up element is used, because the incident angle on the image pick-up element is too large, the phenomenon (shading) in which a substantial aperture efficiency is reduced on the peripheral part of the image pick-up surface is generated, and the peripheral light amount becomes insufficient.